The invention relates to reducing hair growth in mammals.
Hair proteins include a fairly large quantity of the amino acid cysteine, which includes a thiol (xe2x80x94SH) group. It is the formation of disulfide bonds between cysteine residues in the hair proteins, to form cystine, that give hair its strength and character.
It is known in the art to use depilatory compositions to remove hair from, e.g., legs. Such compositions, when applied to the skin, digest the hair, in part, by breaking down the disulfide bonds in the hair. Such compositions typically include a chemical agent like calcium thioglycolate that aids the digestion process.
We have discovered that the rate of mammalian (including human) hair growth can be reduced by applying a non-depilatory composition including sulfhydryl active compounds to the skin. Sulfhydryl active compounds, as used herein, are compounds that include a free xe2x80x94SH group, thiols without a free xe2x80x94SH group, and thiols or disulfides that can be converted to a moleculer with a free xe2x80x94SH group in cells. Non-depilatory, as used herein, is a composition which after a single topical application does not result in hair removal and/or degradation.
Without being bound to any theory, it is believed that sulfhydryl active compounds reduce hair growth at least in part by one or more of the following mechanisms. During hair growth, cysteine is incorporated into protein chains. The xe2x80x94SH groups of cysteine residues in the protein chains form disulfide bonds (and cystine), binding the protein chains together as part of the normal hair growth. Sulfhydryl active compounds, applied topically, penetrate the hair follicle and interfere with hair growth by (1) reacting with free cysteine to form a mixed cysteine-sulfhydryl active compound disulfide bond, resulting in there being less cysteine available for incorporation into disulfide bonds present in hair proteins; (2) reducing the disulfide bond in cystine in the hair proteins, at the same time forming a mixed cysteine-sulfhydryl active compound disulfide bond; and (3) reducing the disulfide bond in cystine, without concomitant formation of the mixed disulfide bond.
Preferred sulfhydryl active compounds with a free xe2x80x94SH group include thiosalicylic acid, D-cysteine, 2-mercaptoethylamine (cysteamine), captopril, N-acetyl-L-cysteine, cysteinylglycine, 2,3-dimercapto-1-propanesulfonic acid, meso-2,3-dimercaptosuccinic acid, dimethylcysteamine, diethyldithiocarbamic acid, D-penicillamine, L-cysteine methyl ester, and L-cysteine ethyl ester.
Preferred sulfhydryl active compounds without a free xe2x80x94SH group include 3,3xe2x80x2-thiodipropionic acid, isethionic acid, 3-carboxypropyl disulfide, 3,3xe2x80x2-thiodipropionic acid dilauryl ester, sulfasalazine, 3-(methythio)-propylamine, 5xe2x80x2-deoxy-5xe2x80x2-methylthioadenosine, allyl sulfide, DL-xcex1-lipoic acid (reduced form), and DL-methionine-S-methyl-sulfonium chloride.
Preferred sulfhydryl active compounds that are converted to free thiols in cells include phosphocysteamine, which is dephosphorylated to cysteamine in cells; penicillamine disulfide, which is reduced to free penicillamine in cells; and S-2-aminoethyl-L-cysteine, which is hydrolyzed to cysteamine and serine (inactive) in cells.
The sulfhydryl active compounds should not be of too high a molecular weight (greater than about 1000 daltons), or contain highly charged phosphate groups, or compounds that may not adequately penetrate the skin.
The composition contains, in addition to the sulfhydryl active compound, a non-toxic dermatologically acceptable vehicle or carrier which is adapted to be spread on the skin. The concentration of the compound may be varied over a wide range up to a saturated solution, preferably from 1% to 20% by weight. The reduction of hair growth increases as the amount of sulfhydryl active compound applied increases per unit area of skin; the maximum amount that can be effectively applied is limited primarily only by the rate at which the compound penetrates the skin. Generally, the effective amounts range from 100 to 2000. micrograms or more per square centimeter of skin.